DEVELOPING: MasterCard is reportedly investigating a possible breach of cardholder account data involving a U.S.-based payment processor, the company said Friday.

The Wall Street Journal reports that the Purchase, N.Y., credit-card company said law enforcement has been notified of the matter and an "independent data security organization" is conducting an ongoing forensic review.

The company is alerting card-issuing banks regarding "certain MasterCard accounts that are potentially at risk."

"MasterCard's own systems have not been compromised in any manner," a company spokesman told the newspaper.

The spokesman declined to say how many cards may have been compromised or how many banks it is notifying.

The breach was first reported early Friday by Krebs On Security, a blog by former Washington Post reporter Brian Krebs. The blog also reported that Visa was also notifying banks about a breach involving a third-party payment processor.